1. Field of the Invention
The present invention relates to a method and apparatus for treating the surface of a substrate such as a semiconductor wafer with a vaporized treating agent for making the treated surface hydrophobic.
2. Description of the Related Art
In general, a process of manufacturing a semiconductor device comprises the step of forming a photoresist film on a semiconductor wafer. Before formation of the resist film, the wafer surface contacts with moisture in the atmosphere to form OH groups on the wafer surface, with the result that the wafer surface is rendered hydrophilic. If the hydrophilic surface is coated with a resist, the resist film tends to peel off during the developing process because water penetrates into the interface between the wafer surface and the resist film.
To improve the adhesion strength of the resist film, the wafer surface, before coated with a resist, is exposed to an HMDS gas, i.e., a gaseous compound of hexamethyldisilazane, (CH.sub.3).sub.3 SiNHSi(CH.sub.3).sub.3 !, and the OH groups on the wafer surface are replaced with Si(CH.sub.3).sub.3 groups and, thus, to make the wafer surface hydrophobic. This hydrophobic treatment, which is intended to improve the adhesion strength of the resist film, is also called an adhesion treatment.
In the hydrophobic treatment or adhesion treatment, it is necessary to set the HMDS concentration in a carrier gas at an optimum value for preventing the resist film from being peeled off. To achieve the object, it was customary in the past to employ, for example, a method in which the dilution rate or liquid temperature of HMDS is changed, a method in which the quantity of HMDS is changed, a method in which the flow rate of a vaporizing carrier gas (N.sub.2 gas) of HMDS is changed, or a method in which the vaporizing area of HMDS is changed by utilizing a capillary action.
However, in the conventional method in which the dilution rate or liquid temperature of HMDS is changed, it is difficult to maintain a satisfactory condition in the treating section because the control section and the treating section are positioned relatively apart from each other. When it comes to, particularly, the method in which the liquid temperature of HMDS is controlled, the control section is rendered bulky and complex. In addition, the control operation is troublesome. Further, in the conventional methods in which the flow rate of HMDS is changed, in which the flow rate of the N.sub.2 gas for vaporizing HMDS is changed, and in which the vaporizing area of HMDS is changed, it is difficult to achieve a subtle control, resulting in failure to prevent sufficiently the resist film from being peeled off.